Grace, one important thing to understand about every single .net page is it already has a form. This means a couple things to you. First, you cannot add a form  tag to your custom module because the aspx page already has one and only a single form is available per page. So, this means you need to use the built in form to do the typical POST/GET you are talking about. The client API makes it possible for you to use/find the form exposed in the default.aspx for your usage. I would look to the client api docs to get you started.

You could create a custom aspx page but this is a security concern. Also, there is some form controls available by Paul Wilson which may aide you if necessary still after looking at client api.